Microwave-assisted magnetic recording apparatus and method

ABSTRACT

A magnetic recording medium includes a recording surface comprising a first recording layer having a first ferromagnetic resonant frequency and a second recording layer having a second ferromagnetic resonant frequency. The first recording layer is configured for storing user data and the second recording layer configured for storing servo data. A recording head arrangement is configured for microwave-assisted magnetic recording (MAMR) and writing user data to the first recording layer. The recording head arrangement comprises a write pole configured to generate a write magnetic field, and a write-assist arrangement proximate the write pole. The write-assist arrangement is configured to generate a radiofrequency assist magnetic field at a frequency that corresponds to the first ferromagnetic resonant frequency. A reader of the recording head arrangement is configured to read combined signals from the first and second recording layers.

RELATED PATENT DOCUMENTS

This application is a continuation of U.S. patent application Ser. No.16/249,438, filed Jan. 16, 2019, which is a continuation of U.S. patentapplication Ser. No. 16/013,193, filed Jun. 20, 2018, now U.S. Pat. No.10,249,332, which are incorporated herein by reference in theirentireties.

SUMMARY

Embodiments are directed to an apparatus including a magnetic recordingmedium having a recording surface comprising a first recording layerhaving a first ferromagnetic resonant frequency and a second recordinglayer having a second ferromagnetic resonant frequency. The firstrecording layer is configured for storing user data and the secondrecording layer configured for storing servo data. A recording headarrangement is configured for microwave-assisted magnetic recording(MAMR) and writing user data to the first recording layer. The recordinghead arrangement comprises a write pole configured to generate a writemagnetic field, and a write-assist arrangement proximate the write pole.The write-assist arrangement is configured to generate a radiofrequencyassist magnetic field at a frequency that corresponds to the firstferromagnetic resonant frequency. A reader of the recording headarrangement is configured to read combined signals from the first andsecond recording layers.

Embodiments are directed to an apparatus including a magnetic recordingmedium comprising a first recording surface and an opposing secondrecording surface. The first recording surface comprises a firstrecording layer configured for storing user data and having a firstferromagnetic resonant frequency, and a second recording layerconfigured for storing servo data and having a second ferromagneticresonant frequency. The second recording surface comprises a thirdrecording layer configured for storing user data and having a thirdferromagnetic resonant frequency, and a fourth recording layerconfigured for storing servo data and having a fourth ferromagneticresonant frequency. A first recording head arrangement is configured forMAMR and writing user data to the first recording layer. The firstrecording head arrangement comprises a first write pole configured togenerate a write magnetic field, and a first write-assist arrangementproximate the first write pole. The first write-assist arrangement isconfigured to generate a radiofrequency assist magnetic field at afrequency that corresponds to the first ferromagnetic resonantfrequency. The first recording head arrangement comprises a first readerconfigured to read combined signals from the first and second recordinglayers. A second recording head arrangement is configured for MAMR andwriting user data to the third recording layer. The second recordinghead arrangement comprises a second write pole configured to generate awrite magnetic field, and a second write-assist arrangement proximatethe second write pole. The second write-assist arrangement is configuredto generate a radiofrequency assist magnetic field at a frequency thatcorresponds to the third ferromagnetic resonant frequency. The secondrecording head arrangement comprises a second reader configured to readcombined signals from the third and fourth recording layers.

Embodiments are directed to a method comprising moving a recording headarrangement configured for MAMR relative to a magnetic recording medium.The magnetic recording medium includes a recording surface comprising afirst recording layer having a first ferromagnetic resonant frequencyand a second recording layer having a second ferromagnetic resonantfrequency. The second recording layer is configured for storing servodata. The method comprises generating a radiofrequency assist magneticfield having a frequency that corresponds to the first ferromagneticresonant frequency. The method also comprises generating a write fieldto write user data to the first recording layer assisted by the assistmagnetic field. The method further comprises reading combined signalsfrom the first and second recording layers.

The above summary is not intended to describe each disclosed embodimentor every implementation of the present disclosure. The figures and thedetailed description below more particularly exemplify illustrativeembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the specification reference is made to the appended drawings,where like reference numerals designate like elements, and wherein:

FIG. 1 illustrates a portion of a track of a typical magnetic recordingmedium which includes data sectors embedded with servo data;

FIG. 2A is a downtrack sectional view of a magnetic recording mediumhaving a recording surface comprising multiple recording layers withdifferent ferromagnetic resonant frequencies for separately storingservo data and user data in accordance with various embodiments;

FIG. 2B is a downtrack sectional view of a magnetic recording mediumhaving a recording surface comprising multiple recording layers withdifferent ferromagnetic resonant frequencies for separately storingservo data and user data in accordance with various embodiments;

FIG. 2C is a downtrack sectional view of a magnetic recording mediumhaving a recording surface comprising multiple recording layers withdifferent ferromagnetic resonant frequencies for separately storingservo data and user data in accordance with various embodiments;

FIG. 2D is a cross-track sectional view of a magnetic recording mediumhaving a recording surface comprising multiple recording layers withdifferent ferromagnetic resonant frequencies for separately storingservo data and user data in accordance with various embodiments;

FIG. 3A is a downtrack sectional view of a magnetic recording mediumhaving a recording surface comprising multiple recording layers withdifferent ferromagnetic resonant frequencies for separately storingservo data and user data in accordance with various embodiments;

FIG. 3B shows the magnetic recording medium of FIG. 3A incorporated in ahard disk drive for use in the field;

FIG. 4 is a downtrack sectional view of a magnetic recording mediumhaving opposing recording surfaces each comprising multiple recordinglayers with different ferromagnetic resonant frequencies for separatelystoring servo data and user data in accordance with various embodiments.

FIG. 5 illustrates components of a hard disk drive including a readchannel for processing combined servo and user data readback signalsobtained from multiple recording layers with different ferromagneticresonant frequencies in accordance with various embodiments;

FIG. 6 illustrates a method of writing data to and reading data from amagnetic recording surface comprising recording layers with differentferromagnetic resonant frequencies for separately storing servo and userdata in accordance with various embodiments;

FIG. 7A shows a recording head arrangement configured for MAMR inaccordance with various embodiments;

FIG. 7B shows a spin-torque oscillator of the write-assist arrangementillustrated in FIG. 7A;

FIG. 8 is a block diagram of a data storage apparatus configured towrite data to and read data from a magnetic recording surface comprisingrecording layers with different ferromagnetic resonant frequencies forseparately storing servo and user data in accordance with variousembodiments.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part of the description hereof and in which areshown by way of illustration several specific embodiments. It is to beunderstood that other embodiments are contemplated and may be madewithout departing from the scope of the present disclosure. Thefollowing detailed description, therefore, is not to be taken in alimiting sense.

Disk drives are data storage devices that store digital data in magneticform on a rotating storage medium. Modern disk drives comprise of one ormore rigid data disks that are coated with a magnetizable medium andmounted on the hub of a spindle motor for rotation at a constant highspeed. An array of recording transducers, referred to as data heads orheads, are mounted to an actuator arm, and a servo system is used tomove the actuator arm such that a particular head is positioned over adesired location for reading or writing information to and from thedisk. During a write operation, the head writes data onto the disk andduring a read operation the head senses the data previously written onthe disk and transfers the information to an external environment.

Data on the data disk is typically stored on concentric circular tracksalong the surface of the disk. Often, the disk is divided into severaldisk zones which contain regions of adjacent tracks with a commonrecording bit rate. A typical disk drive configuration interspersesservo information at various points along each track for maintainingaccurate head positioning over the disk. Servo information is typicallywritten to each track in designated servo burst sectors and divides eachdisk track into slices called data wedges. As the disk rotates, the headreads the servo information contained in the servo bursts and sends theservo information back to the servo system to make any necessaryposition adjustments to the actuator arm.

FIG. 1 illustrates a portion of a track 101 of a typical magneticrecording medium which includes data sectors embedded with servo data.Every track 101 may be divided into discrete data sectors containingpackets of user data. A data sector generally contains a user data fieldthat is encapsulated with servo data to help identify and process theuser data. The aerial density capability (ADC) of the magnetic recordingmedium is determined by a number of factors, including the track densitykTPI (tracks per inch), the bit density kBPI (bits per inch), therecording area (RA), and the format efficiency (FE). The biggestcontributor to format efficiency loss is due to the servo wedges,particularly in the case of a data sector split. For example, a servowedge as shown in FIG. 1 includes GAS (gap after servo), servo data(servo), GBS (gap before servo), and a data sector split 102.

Because data sector fields are typically fixed-length fields, they maybe required to split across a servo region 103 when an integer number ofdata sectors cannot fit within a data wedge. When a data sector split102 occurs, a portion 104 of the data sector is located before the servoregion 103 and another portion 106 of the data sector is located afterthe servo region 103. The format efficiency loss due to data sectorsplits 102 is substantial. In general, knowing which data sectors aresplit and where in the data sectors a split occurs is required forlocating desired data on the data disk. One conventional method oftracking data sector splits on a disk is to store information aboutevery data sector split occurrence in memory. The information storedabout a split data sector may include the sector's zone location, datawedge number, sector number, and split count (where in the data sectorthe split occurs).

Data sector split information is typically determined and recorded inmemory during the disk drive manufacturing process. By storing suchinformation about each data sector split occurrence, accurate locationof data on the disk drive is achieved. A drawback of storing informationabout every data sector split occurrence is that the memory required tostore such information can be very large. Modern disk drives typicallycontain many thousands of split data sectors, and storing several dataentries for each split data sector requires substantial memory.Reserving large amounts of memory for storing data sector splits mayraise the production cost of the disk drive, consume the drive'sresources, and slow the drive's performance.

Improving the format efficiency of a magnetic recording medium isdifficult because the track density and format efficiency are inverselycompeting against each other on a single recording surface. For example,increasing the number of servo wedges on a single recording surfaceimproves the servo-on-track capability for higher track densities, butit reduces the format efficiency. It is not possible to maximize servowedge numbers and format efficiency on a single layer recording surface.

Embodiments of the disclosure are directed to systems and methods forincreasing the aerial density capability of a magnetic recording system(e.g., a HDD). More particularly, embodiments of the disclosure aredirected to systems and methods for increasing the aerial densitycapability of a magnetic recording system configured formicrowave-assisted magnetic recording. According to various embodiments,the aerial density capability of a magnetic recording system can beincreased by increasing (e.g., maximizing) the format efficiency using arecording head arrangement and a magnetic recording medium configuredfor microwave—assisted magnetic recording.

Embodiments of the disclosure are directed to magnetic recording systemsthat employ high-frequency assisted writing using a spin-torqueoscillator (STO). This type of recording (e.g., microwave-assistedmagnetic recording (MAMR)) applies a high frequency oscillatory assistmagnetic field from the STO to the magnetic grains of the recordinglayer during a write operation. The assist field has a frequency thesame as or close to the resonant frequency of the magnetic grains in therecording layer to facilitate the switching of the magnetization of thegrains at lower write fields from the conventional write head than wouldotherwise be possible without assisted recording. MAMR provides for anincrease in the coercivity of the magnetic recording layer above thatwhich could be written to by using conventional perpendicular magneticrecording alone. The increase in coercivity afforded by MAMR allows fora reduction in the size of the magnetic grains and thus a correspondingincrease in recording density of the recording medium.

FIG. 2A is a downtrack sectional view of a magnetic recording medium 202having a recording surface 204 comprising multiple recording layers eachhaving a different ferromagnetic resonant frequency in accordance withvarious embodiments. According to the embodiment shown in FIG. 2A, therecording surface 204 includes a first recording layer 206 comprisingmagnetic material having a first ferromagnetic resonant frequency, f₁.The recording surface 204 includes a second recording layer 208comprising magnetic material having a second ferromagnetic resonantfrequency, f₂. In FIG. 2A and other figures, it is understood that thefirst ferromagnetic resonant frequency, f₁, is different from the secondferromagnetic resonant frequency, f₂. The first recording layer 206 isonly writable when stimulated with write-assist energy at or near thefirst frequency, f₁. The second recording layer 208 is only writablewhen stimulated with write-assist energy at or near the secondfrequency, f₂. According to various embodiments, the first recordinglayer 206 is configured for storing user data, and the second recordinglayer 208 is configured for storing servo data. It is understood that,in some embodiments, the first recording layer 206 can be configured forstoring servo data, and the second recording layer 208 can be configuredfor storing user data. In either configuration, the recording layer thatstores user data is devoid of servo data.

FIG. 2B is a downtrack sectional view of a magnetic recording medium 212having a recording surface 214 comprising multiple recording layers eachhaving a different ferromagnetic resonant frequency in accordance withvarious embodiments. The recording surface 214 includes a firstrecording layer 216 comprising magnetic material having a firstferromagnetic resonant frequency, f₁, and a second recording layer 218comprising magnetic material having a second ferromagnetic resonantfrequency, f₂. In the embodiment shown in FIG. 2B, servo data is writtento the second recording layer 218 using a MAMR recording head configuredto generate a radiofrequency (RF) assist magnetic field at a frequencythat corresponds to the second ferromagnetic resonant frequency, f₂.Writing servo data to the second recording layer 218 of the recordingsurface 214 is typically performed at the factory, such as during mediaprocessing or drive factory testing. With the servo data written to thesecond recording layer 218, the first recording layer 216 of therecording surface 214 can now be used to store user data.

FIG. 2C is a downtrack sectional view of a magnetic recording medium 222having a recording surface 224 comprising multiple recording layers eachhaving a different ferromagnetic resonant frequency in accordance withvarious embodiments. The recording surface 224 includes a firstrecording layer 226 comprising magnetic material having a firstferromagnetic resonance frequency, f₁, and a second recording layer 228comprising magnetic material having a second ferromagnetic resonantfrequency, f₂. In the embodiment shown in FIG. 2C, servo data written tothe second recording layer 228 is read to properly position a MAMRrecording head, and user data is written to the first recording layer226 using the MAMR recording head configured to generate an RF assistedmagnetic field at a frequency that corresponds to the firstferromagnetic resonant frequency, f₁. Writing user data to the firstrecording layer 226 of the recording surface 224 is typically performedin the field (e.g., at a data center). FIG. 2D is a cross-tracksectional view of the magnetic recording medium 222 shown in FIG. 2Clooking in the plane of the medium 222 across four discrete tracks, T₁,T₂, T₃, and T₄. Each track includes user data written to the firstrecording layer 226 and servo data written to the second recording layer228.

In the embodiments shown in FIGS. 2A-2D, all servo wedges that wouldconventionally be interspersed within user data on the first recordinglayer 206, 216, 226 are instead moved from the first recording layer206, 216, 226 onto the second recording layer 208, 218, 228 of the samerecording surface 204, 214, 224. A significant increase in data storagecapacity is achieved by moving all servo wedges from the first recordinglayer 206, 216, 226 to the second recording layer 208, 218, 228. Servodata can be written to the second recording layer 208, 218, 228 at amuch higher density than that on normal perpendicular magnetic recording(PMR) media to achieve higher track densities (kTPI) and aerial densitycapability (ADC). This results from the much larger surface area that isavailable on the second recording layer 208, 218, 228 relative to thaton current embedded servo recording media. The ADC of the magneticrecording medium 202, 212, 222 is increased by increasing the trackdensity capability through increasing servo wedge numbers on the secondrecording layer 208, 218, 228.

FIG. 3A is a downtrack sectional view of a magnetic recording mediumhaving a recording surface comprising multiple recording layers withdifferent ferromagnetic resonant frequencies for separately storingservo data and user data in accordance with various embodiments. FIG. 3Ashows a magnetic recording medium 302 having a recording surface 304positioned in proximity to a recording head arrangement 312. Therecording surface 304 includes a first recording layer 306 having afirst ferromagnetic resonant frequency, f₁, and a second recording layer308 having a second ferromagnetic resonant frequency, f₂. The recordinghead arrangement 312 includes a write pole 314 configured to generate awrite magnetic field and a write-assisted arrangement 316 proximate thewrite pole 314. In the embodiment shown in FIG. 3A, the recording headarrangement 312 is a component of a servo writer configured to writeservo data 310 to the second recording layer 308 (e.g., at the factory).The write-assist arrangement 316 is configured to generate aradiofrequency assist magnetic field at a frequency that corresponds tothe second ferromagnetic resonant frequency, f₂. After completing theservo writing process and other processes at the factory, the magneticrecording medium 302 shown in FIG. 3A can be installed in a hard diskdrive for use in the field.

FIG. 3B shows the magnetic recording medium 302 of FIG. 3A incorporatedin a hard disk drive for use in the field. FIG. 3B shows the recordingsurface 304 of the magnetic recording medium 302 in proximity to arecording head arrangement 332. The recording head arrangement 332includes a write pole 334 configured to generate a write magnetic fieldand a write-assist arrangement 336 proximate the write pole 334. In theembodiment shown in FIG. 3B, the recording head arrangement 332 isconfigured to write user data 320 to the first recording layer 306. Thewrite-assist arrangement 336 is configured to generate a radiofrequencyassist magnetic field at a frequency that corresponds to the firstferromagnetic resonant frequency, After user data 320 has been writtento the first recording layer 306, a reader 340 of the recording headarrangement 332 is configured to read combined signals (user data andservo data) from the first and second recording layers 306, 308. As willbe described below, the combined signals read by the reader 340 can befiltered and separated into a user data signal and a servo data signal.

FIG. 4 is a downtrack sectional view of a magnetic recording mediumhaving opposing recording surfaces each comprising multiple recordinglayers with different ferromagnetic resonant frequencies for separatelystoring servo data and user data in accordance with various embodiments.FIG. 4 shows a magnetic recording medium 402 having a first recordingsurface 404 and an opposing second recording surface 444. The firstrecording surface 404 includes a first recording layer 406 having afirst ferromagnetic resonant frequency, f₁, and a second recording layer408 having a second ferromagnetic resonant frequency, f₂. The secondrecording surface 444 includes a third recording layer 446 having athird ferromagnetic resonant frequency, f₃, and a fourth recording layer448 having a fourth ferromagnetic resonant frequency, f₄. In someembodiments, the third and fourth ferromagnetic resonant frequencies, f₃and f₄, can be the same as the first and second ferromagnetic resonantfrequencies, f₁ and f₂, respectively. In other embodiments, the thirdand fourth ferromagnetic resonant frequencies, f₃ and f₄, can bedifferent from the first and second ferromagnetic resonant frequencies,f₁ and f₂, respectively.

A first recording head arrangement 412 is positioned proximate the firstrecording surface 404, and a second recording head arrangement 452 ispositioned proximate the second recording surface 444. The firstrecording head arrangement 412 includes a write pole 414 configured togenerate a write magnetic field and a write-assist arrangement 416proximate the write pole 414. The write-assist arrangement 416 isconfigured to generate a radiofrequency assist magnetic field at afrequency that corresponds to the first ferromagnetic resonantfrequency, f₁. The first recording head arrangement 412 includes areader 418 configured to read combined signals from the first and secondrecording layers 406, 408 of the first recording surface 404. The secondrecording head arrangement 452 includes a write pole 454 configured togenerate a write magnetic field and a write-assist arrangement 456proximate the write pole 454. The write-assist arrangement 456 isconfigured to generate a radiofrequency assist magnetic field at afrequency corresponding to the third ferromagnetic resonant frequency,f₃. The second recording head arrangement 452 includes a reader 458configured to read combined signals from the first and second recordinglayers 446, 448 of the second recording surface 444.

FIG. 5 illustrates components of a hard disk drive including a readchannel for processing combined servo and user data readback signalsobtained from multiple recording layers with different ferromagneticresonant frequencies in accordance with various embodiments. The harddisk drive 500 includes a magnetic recording medium 502 having arecording surface 504 comprising a first recording layer 506 and asecond recording layer 508. The first recording layer 506 comprisesmagnetic material having a first ferromagnetic resonant frequency, f₁,and the second recording layer 508 comprises magnetic material having asecond ferromagnetic resonant frequency, f₂. User data is stored on thefirst recording layer 506, and servo data is stored on the secondrecording layer 508. A reader 510 is configured to sense the magneticflux from the recording surface 504 and generates an analog readbackwaveform comprising combined signals read from the first and secondrecording layers 506, 508. The user data signals read from the firstrecording layer 506 and the servo data signals read from the secondrecording layer 508 have very different frequencies. For example, theuser data signals typically have signal content at a frequency of about2 GHz. The servo data signals typically have signal content at afrequency of about 200 MHz. This large frequency gap between the userdata signals and the servo data signals can be readily differentiated bythe read channel 514.

The combined readback signals 511 are communicated from the reader 510,to a preamplifier 512, and to an analog front end 516 of the readchannel 514. The combined readback signals 511 are sampled by ananalog-to-digital converter (ADC) 518. The samples produced by the ADC518 are passed to a high-pass filter 520 and to a low pass filter 530.The high-pass filter 520 is configured to pass signal content of thecombined readback signals 511 corresponding to the higher frequency userdata signals. The higher frequency user data signals are communicatedfrom the high-pass filter 520 to a Viterbi detector (e.g., SOVA) 522,the output of which corresponds to user data signals. The low passfilter 530 is configured to pass signal content of the combined readbacksignals 511 corresponding to the lower frequency servo data signals. Thelower frequency servo data signals are communicated from the low-passfilter 530 to a servo demodulator 532, the output of which correspondsto servo data signals communicated to the servo system of the hard diskdrive 500. It is noted that the magnetic recording medium 502 caninclude two opposing recording surfaces (see FIG. 4), and that aseparate read channel 514 is provided for processing combined servo anduser data readback signals obtained from the opposing recording surface.

FIG. 6 illustrates a method of writing data to and reading data from amagnetic recording surface comprising recording layers with differentferromagnetic resonant frequencies for separately storing servo and userdata in accordance with various embodiments. The method shown in FIG. 6involves moving 602 a recording head arrangement configured for MAMRrelative to a magnetic recording medium having a recording surfacecomprising a first recoding layer and a second recording layer. Thefirst recording layer has a first ferromagnetic resonant frequency, andthe second recording layer has a second ferromagnetic resonantfrequency. The second recording layer is configured for storing servodata. The method involves generating 604 a radiofrequency assistmagnetic field having a frequency that corresponds to the firstferromagnetic resonant frequency. The method also involves generating606 a write field to write user data to the first recording layerassisted by the assist magnetic field. The method further involvesreading 608 combined signals from the first and second recording layers.The method may also involve separating 610 the combined signals into auser data signal and a servo data signal.

FIG. 7A shows a recording head arrangement configured for MAMR inaccordance with various embodiments. The recording head arrangement 700includes a writer 730 and a reader 720 proximate an air bearing surface(ABS) 701 for respectively writing and reading data to/from a magneticrecording medium 750. The magnetic recording medium 750 includes arecording surface 752 comprising a first recording layer 754 and asecond recording layer 756. The first recording layer 754 comprisesmagnetic material having a first ferromagnetic resonant frequency, f₁,and the second recording layer 756 comprises magnetic material having asecond ferromagnetic resonant frequency, f₂. User data is stored on thefirst recording layer 754, and servo data is stored on the secondrecording layer 756.

The writer 730 includes a write pole 732 coupled to a return pole 731and, in accordance with some embodiments, an axillary return pole 734.Although not shown in FIG. 7A, the auxiliary return pole 734 is coupledto the write pole 732 by way of a magnetic via. The writer 730 is shownpositioned proximate a write coil arrangement 708. In the embodimentshown in FIG. 7A, the write coil arrangement 708 includes an upper coil712 and a lower coil 710 (e.g., double-layer pancake coil design). Inother embodiments, a single coil or helical coil design can be usedinstead of a double-layer pancake coil design. The reader 720 comprisesa reader element 726 (e.g., giant magnetoresistance (GMR) sensor)disposed between a pair of reader shields 722 and 724.

The recording head arrangement 700 also includes a write-assistarrangement 740 positioned proximate the write pole 732. For example,the write-assist arrangement 740 can be positioned in the gap betweenthe write pole 732 and the return pole 731, and is preferably situatedadjacent the write pole 732. The write-assist arrangement 740 isconfigured to generate a radiofrequency assist magnetic field at afrequency corresponding to the first ferromagnetic resonant frequency,f₁ of the first recording layer 754. As is shown in FIG. 7B, thewrite-assist arrangement 740 includes an STO 742 configured to generatea first write-assist field having a first frequency f₁ (WAF-f₁). Whenwriting to tracks having the first ferromagnetic resonant frequency, f₁,on the first recording layer 754, the STO 742 is energized by input of adrive current, I_(i), at the appropriate time (e.g., preceding orconcurrently with the write current).

FIG. 8 is a block diagram of a data storage apparatus 800 (e.g., a HDD)configured to write data to and read data from a magnetic recordingsurface comprising recording layers with different ferromagneticresonant frequencies for separately storing servo and user data inaccordance with various embodiments. The data storage apparatus 800includes a control logic circuit 802 which includes a data controller804 that processes read and write commands and associated data from ahost device 806. The host device 806 may include any electronic devicethat can be communicatively coupled to store and retrieve data from adata storage device, e.g., a computer. The data controller 804 iscoupled to a read/write channel 808 and configured to read data from andwrite data to a recording surface 811 of a magnetic disk 810. Therecording surface 811 includes a first recording layer 813 having afirst ferromagnetic resonant frequency, f₁, and a second recording layer815 having a second ferromagnetic resonant frequency, f₂. Servo data isstored on the second recording layer 815, and user data is stored on thefirst recording layer 813.

The read/write channel 808 generally converts data between the digitalsignals processed by the data controller 804 and the analog signalsconducted through one or more read/write heads 812 configured for MAMR.The read/write channel 808 also provides servo data read from servowedges 814 on the second recording layer 815 of the magnetic disk 810 toa servo controller 816. The servo controller 816 uses the servo dataread from the second recording layer 815 to drive an actuator 818 (e.g.,voice coil motor, or VCM and/or micro-actuator) that rotates an arm 820upon which the read/write heads 812 are mounted.

Data within the servo wedges 814 on the second recording layer 815 canbe used to detect the location of the read/write head 812. The servocontroller 816 uses servo data read from the second recording layer 815to move the read/write head 812 to an addressed track 822 and block onthe first recording layer 813 in response to the read/write commands(seek mode). While user data is being written to and/or read from thefirst recording layer 813, servo data is concurrently read from thesecond recording layer 815 and used to maintain the read/write head 812in alignment with the track 822 (track following mode).

Although two separate controllers 804 and 816 and a read/write channel808 have been shown for purposes of illustration, it is to be understoodthat their functionality described herein may be integrated within acommon integrated circuit package or distributed among more than oneintegrated circuit package. Similarly, a head/disk assembly can includea plurality of data storage disks 810, an actuator arm 820 with aplurality of read/write heads 812 (or other sensors) which are movedradially across different recording surfaces 811 of the disk(s) 810 bythe actuator motor 818 (e.g., voice coil motor), and a spindle motor(not shown) which rotates the disks 810.

In some embodiments, a magnetic recording medium having a magneticrecording surface comprising recording layers with differentferromagnetic resonant frequencies for separately storing servo and userdata can be configured for perpendicular magnetic recording (PMR). Inother embodiments, a magnetic recording medium having a magneticrecording surface comprising recording layers with differentferromagnetic resonant frequencies for separately storing servo and userdata can be configured for bit patterned magnetic recording (BPMR). ABPMR medium provides patterns of magnetic regions (e.g., “dots”,“islands” or “blocks”) within non-magnetic material (e.g., “troughs”).In bit patterned media, the magnetic material on a disk is patternedinto small isolated islands such that there is a single magnetic domainin each island or “bit”. The single magnetic domains can be a singlegrain or a few strongly coupled grains that switch magnetic states inconcert as a single magnetic volume. To produce the required magneticisolation of the patterned islands, the regions between the islands(e.g., troughs) are essentially nonmagnetic. According to variousembodiments, the ferromagnetic resonant frequency of a particular track(discrete or bit patterned) of a magnetic recording medium can rangebetween about 10 GHz and 40 GHz, such as between 20 GHz and 30 GHz.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations can besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present disclosure. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisdisclosure be limited only by the claims and the equivalents thereof.All references cited within are herein incorporated by reference intheir entirety.

1. An apparatus, comprising: a magnetic recording medium comprising aplurality of recording layers, each of the plurality of recording layershaving a different ferromagnetic resonant frequency; and a recordinghead arrangement configured for microwave-assisted magnetic recording(MAMR) and writing data to the plurality of recording layers, therecording head arrangement configured to generate a radiofrequencyassist magnetic field at a frequency that corresponds to each of thedifferent ferromagnetic resonant frequencies of the plurality ofrecording layers.
 2. The apparatus of claim 1, wherein the magneticrecording medium comprises more than two recording layers.
 3. Theapparatus of claim 1, wherein the magnetic recording medium comprises atleast three recording layers.
 4. The apparatus of claim 1, wherein themagnetic recording medium comprises at least four recording layers. 5.The apparatus of claim 1, wherein the plurality of recording layers aredistributed on a same recording surface of the magnetic recordingmedium.
 6. The apparatus of claim 1, wherein the plurality of recordinglayers are distributed on two opposing recording surfaces of themagnetic recording medium.
 7. The apparatus of claim 1, wherein at leasttwo of the plurality of recording layers are configured to store userdata.
 8. The apparatus of claim 1, wherein at least one of the pluralityof recording layers is configured to store servo data.
 9. The apparatusof claim 1, wherein the recording head arrangement comprises: a writepole arrangement configured to generate write magnetic fields; and awrite-assist arrangement proximate the write pole arrangement, thewrite-assist arrangement configured to generate the radiofrequencyassist magnetic fields at frequencies that correspond to the differentferromagnetic resonant frequencies of the plurality of recording layers.10. An apparatus, comprising: a magnetic recording medium comprising aplurality of recording layers, each of the plurality of recording layershaving a different ferromagnetic resonant frequency; a recording headarrangement configured for microwave-assisted magnetic recording (MAMR)and writing data to the plurality of recording layers, the recordinghead arrangement configured to generate a radiofrequency assist magneticfield at a frequency that corresponds to each of the differentferromagnetic resonant frequencies of the plurality of recording layers;a reader arrangement configured to read signals from the plurality ofrecording layers; and a channel coupled to the reader arrangement andcomprising a filter arrangement, the filter arrangement configured toseparate user data signals from the signals read by the readerarrangement.
 11. The apparatus of claim 10, wherein the filterarrangement is configured to separate servo data signals from thesignals read by the reader arrangement.
 12. The apparatus of claim 10,wherein the magnetic recording medium comprises more than two recordinglayers.
 13. The apparatus of claim 10, wherein the magnetic recordingmedium comprises at least three recording layers.
 14. The apparatus ofclaim 10, wherein the magnetic recording medium comprises at least fourrecording layers.
 15. The apparatus of claim 10, wherein the pluralityof recording layers are distributed on a same recording surface of themagnetic recording medium.
 16. The apparatus of claim 10, wherein theplurality of recording layers are distributed on two opposing recordingsurfaces of the magnetic recording medium.
 17. The apparatus of claim10, wherein at least two of the plurality of recording layers areconfigured to store user data.
 18. The apparatus of claim 10, wherein atleast one of the plurality of recording layers is configured to storeservo data.
 19. The apparatus of claim 10, wherein the recording headarrangement comprises: a write pole arrangement configured to generatewrite magnetic fields; and a write-assist arrangement proximate thewrite pole arrangement, the write-assist arrangement configured togenerate the radiofrequency assist magnetic fields at frequencies thatcorrespond to the different ferromagnetic resonant frequencies of theplurality of recording layers.
 20. A method, comprising: moving arecording head arrangement configured for microwave-assisted magneticrecording (MAMR) relative to a magnetic recording medium, the magneticrecording medium comprising a plurality of recording layers each havinga different ferromagnetic resonant frequency; generating, using therecording head arrangement, radiofrequency assist magnetic fields havingfrequencies that correspond to the different ferromagnetic resonantfrequencies of the plurality of recording layers; generating writefields; and writing data to the plurality of recording layers using thewrite fields and the assist magnetic fields.